Neuraminidase cleaves terminal sialic acid residues from glycoproteins, glycolipids and oligosaccharides. They can be found as one of two glycoproteins on the surface of influenza viruses, where its role is thought to be in releasing progeny virus particles from infected cells, as well as in breaking down the mucosal lining of the upper respiratory tract during initial infection. Mammalian and trypanosomal neuraminidases (sialidases) have been identified. The native structure of Salmonella typhimurium sialidase (STNA), which has 381 amino acids, has been solved previously and the model refined to a resolution of 1.05 E with a crystallographic R value of 9.8% and a free R value of 13.2% using SHELXL. An active site mutant (D62G) and an inhibitor-enzyme complex were crystallized and data collected at BL9-1 to resolutions of 0.92 E and 0.79 E, respectively. Data quality was continuously monitored using the real-time data processing environment available at BL9-1. Electron density maps were calculated immediately at the end of the data collection showing that the inhibitor was bound in the active site. Even this first difference map was of such high quality that carbon, nitrogen and oxygen atoms could be unambiguously identified.